Indexed on: 22 Jun '08Published on: 22 Jun '08Published in: Glass Physics and Chemistry
The concentration dependence of the electrical conductivity of glasses in the Tl2O-B2O3 system is studied. The nature of charge carriers in this system is experimentally investigated for the first time. It is demonstrated using the Hittorf, Tubandt, and Hebb-Liang-Wagner techniques and the Faraday law that neither Tl+ ions nor electrons are involved in the electricity transport. The verification of the Faraday law does not reveal the presence of thallium in the amalgam of the cathode or a change in the sample weight after electrolysis, to within the experimental error. This allows one to make the inference that protons can be charge carriers in glasses of the Tl2O-B2O3 system. It is shown using extended X-ray absorption fine structure (EXAFS) spectroscopy that Tl3+ ions and thallium Tl0 reduced to the metallic state are absent in the structure of the glasses under investigation. This means that thallium in glasses of the Tl2O-B2O3 system occurs only in the form of Tl+ ions. The analysis of the IR spectroscopic data leads to only a qualitative conclusion that the water content in the glasses insignificantly increases with an increase in the thallium oxide content. An increase in the electrical conductivity of glasses in the Tl2O-B2O3 system with an increase in the thallium oxide content is explained by the increase in the number of protons formed upon dissociation of H+[BO4/2]− structural-chemical units, because their concentration increases with increasing Tl2O content. In the structure of boron oxide, impurity hydrogen enters predominantly into the composition of H+[O2/2BO−] structural-chemical units, for which the dissociation energy is higher than that for the H+[BO4/2]− structural-chemical units. The increase in the concentration of H+[BO4/2]− structural-chemical units is accompanied by the increase in the number of dissociated protons, which are charge carriers in glasses of the Tl2O-B2O3 system.